The present invention relates to an array ultrasonic transducer used for an ultrasonodiagnosis system, a nondestructive testing equipment, an ultrasonic therapy system, or the like.
As an ultrasonic transducer capable of electronic focusing or electronic scanning using an ultrasonic beam, an array ultrasonic transducer is known. For producing a typical ultrasonic array transducer, a piezoelectric plate, which has electrodes on both faces and which has been subjected to poling, is formed into a row of fine strip-shaped elements by dicing. Conversion between an ultrasonic wave and an electric signal is conducted by the thickness mode vibration of respective elements. However, the spatial resolution demanded by the ultrasonodiagnosis and the ultrasonic measurement has recently become higher. Thus, the required strip forming technology is approaching the limitation as described below. For attaining higher resolution, it is necessary to raise the ultrasonic frequency and the number of elements used for transmission and reception of the ultrasonic waves. In both of these cases, the width of the above described elements must be made small, resulting in a difficult problem for strip dicing.
Attempts to obtain a transducer capable of electronic scanning or electronic focusing without conducting dicing are described in Japanese Patent Unexamined Publication No. 58-156295 (1983), for example. In a transducer of this type, a large number of split electrodes are formed on the surface of the piezoelectric plate in an array form. The area of each electrode is used as a transducer element. The transducer of this type is hereafter referred to as an ultrasonic transducer of monolithic array type.
Since in the transducer of monolithic array type it is easy to reduce the width of the element to reduce the element spacing, the transducer of monolithic array type is suitable to a high frequency signal and is promising as a transducer for obtaining an image with high resolution. In the transducer of this type, however, an ultrasonic wave of one mode is propagated within the piezoelectric plate in its lengthwise direction while being reflected by the first and second faces of the piezoelectric plate, resulting in an unwanted response. Accordingly, such represent a disadvantage which may be incurred in practical use.